a) Field of the Invention
The present invention relates to an optical head assembly for recording to/reproducing from optical recording media. In particular the present invention relates to an optical head assembly that performs feedback control for the light emitting amount of a laser light source (light intensity) by directly detecting a portion of laser light rays emitted from the laser light source toward the optical recording medium.
b) Description of the Related Art
In the optical head assembly for recording to/reproducing from optical recording media such as CD and DVD, the amount of laser light emitted from a laser light source greatly fluctuates depending on temperature and elapse. Therefore, it is necessary to perform feedback control for the light emitting amount of the laser light source to constantly obtain a predetermined output of emission from the laser light source.
Known as a method for controlling light emitting amount of the laser light source is a technique that directly detects ongoing light rays emitted from the laser light source toward the optical recording medium. Optical head assembly employing this method are disclosed in Patent Publication No. 2543227, Unexamined Japanese Patent Application H2-265036, Japanese Patent Publication H8-7872, Unexamined Japanese Patent Application H3-269835 and the like.
The optical head assembly disclosed in Patent Publication No. 2543227 employs a hologram lens in which a first diffraction area for diffracting returning light rays from an optical recording medium to guide them to an optical detector for signaling and a second diffraction area for reflecting and diffracting, a portion of the ongoing light rays emitted from a laser light source to guide it to an optical detector for monitoring. The second diffraction area of the patent is configured in which a metallic film is coated over a diffraction grating fabricated in the surface of a base substrate.
In the optical head assembly disclosed in Unexamined Japanese Patent Application H2-265036, a hologram lens having almost identical configuration as the above hologram is employed, and an optical detector for signaling and an optical detector for monitoring are formed on the same substrate.
Further, the optical head assembly disclosed in Japanese Patent Publication H8-7872 employs a hologram having only the first diffraction area and an optical element having a predetermined index of reflection, with which the ongoing light is partially reflected toward the optical detector for monitoring. In this optical head assembly also, optical detectors for signaling and monitoring are formed on the same substrate.
In the optical head assembly disclosed in Unexamined Japanese Patent Application H3-269835, the first and second diffraction areas are formed on the surface of a reflection mirror placed halfway on the optical path between the laser light source and the objective lens.